Such a construction has become known from the U.S. Pat. No. 4,174,074, by way of example. From this reference it becomes apparent how the individual agitator tools are fastened to the rings of the rotor and of the milling containers. This is done by soldering in, cementing in place or by srewing the agitator tools into sink borings located on the wall of a ring or by combination of these connection methods.
In the case of such agitator mills these tools serve to impart to the grinding bodies contained in the milling container a positive or reflective motion within a suspension of material to be ground caused by the rotary movement of rotor and milling container relative to each other, which thereby keep on hitting against the agitator tools and cause their heating up.
The agitator tools are frequently bodies of a relatively low cross section, through which they convey the heat absorbed more rapidly into the material to be ground than it can be conveyed to the cooled ring of the milling container or of the rotor.
However, it is precisely this effect which is not desired, since a lot of materials to be ground are thermo-sensitive. For this reason, it has repeatedly been suggested to provide agitator tools with internal cooling (EP-A-0 045 498 and CH-A-658 802).
In the two documents mentioned above there can also be found detailed indications how the agitator tools with internal cooling can be fastened to the rotor or stator pieces of an agitator mill by soldering in or cementing in.
This has already been the case with uncooled agitator tools made up of full material as already described above, or else disk-shaped agitator tools have often merely been clamped to the rotor or stator pieces or held fast by interlocking connections, indentations and projections in their respective positions.
By means of the internal cooling of the agitator tools, the heat generated thereon could be conveyed to the cooling medium in an effective way. However, the construction of the agitator tools with internal cooling has led to another serious problem. If, owing to the high strain, an agitator tool is knocked out of the wall of the milling container or the rotor into which it is built in, with the intermediary layer formed by an adhesive or a solder being removed, this will lead to two highly undesired effects, for, on the one hand, cooling water will ingress into the product to be ground and will render this unserviceable if this material to be ground is sensitive to water, such as chocolate, and, on the other hand, material to be ground may enter the cooling channels, which will call for expensive and long-lasting repairs.
It is an object of the invention to provide an agitator mill in such a manner that the disadvantages associated with tools having internal cooling can be avoided and that the inconvenience caused by the unfavorable heat transmission to the cooling medium in the case of tools made of full material can be eliminated.
Nonetheless, there will still remain the cooling problem, whose solution appears difficult because of the contradicting requirements in the manufacture and use of an agitator mill.